It's the first time myofibrogranuloma, also known as Sandy Flesh disease, has been found in the state, Colorado Parks and Wildlife said.
Officials said the degenerative muscle disease is not believed to be transmittable to humans. However, it is recommended no one consume a walleye they suspect is infected.
According to CPW, the disease typically occurs in the Midwest, particularly in North and South Dakota, Minnesota, Wisconsin and Nebraska. It has spread to the West, including in Utah, Idaho, Wyoming and now Colorado.
"It’s not a shock that it has reached Colorado since it occurs in so many neighboring states, but it is unfortunate," said Carrie Tucker, CPW aquatic biologist in Pueblo. "We don’t expect it to have a big impact because it typically only shows up in a small number of older walleye."
CPW alerts anglers of rare "Sandy Flesh disease" has been found in a walleye taken at Lake Pueblo State Park. The agency urges people to avoid consuming infected fish and to contact CPW. (Colorado Parks and Wildlife)
The disease has existed for decades and typically impacts a few fish in various states, wildlife officials said. It primarily affects older walleye, although there have been a few cases of infected yellow perch.
While fish infected with Sandy Flesh disease look normal on the outside, it can only be found when cleaned.
According to CPW, areas of the filet will look semi-translucent, or yellowish brown, with knotted muscle fibers. The tissue can resemble meat with freezer burn.
"But it’s important that walleye anglers be aware and carefully inspect their catch when they are cleaning them," Tucker said.
Any angler who finds Sandy Flesh in a fish should report it to CPW immediately and provide good, high-resolution photographs so they can be analyzed. If discovered, the entrails should not be thrown back into the lake but disposed of with household waste or buried.
According to wildlife officials, the cause and means of transmission of the disease are unknown.